Solution X is introduced to a solid salt, so that gas Y is given off. Gas Y dissolves in water, forming a solution with a pH below $7$. What could X and Y be?
- AX: aqueous sodium hydroxide; Y: ammonia
- BX: aqueous sodium hydroxide; Y: carbon dioxide
- CX: dilute hydrochloric acid; Y: ammonia
- DX: dilute hydrochloric acid; Y: carbon dioxide